The present invention relates to a protective film for a polarizer, and a polarizing plate, and a visual display using the polarizing plate concerned.
A polarizing plate used for displays, such as liquid crystal display, is a laminated product of a polarizer having a polarization function and a protective film for securing its durability and mechanical strength with the interposition of an adhesive.
The polarization function of the polarizer is obtained by orienting a light anisotropic absorber in a transparent polymer film. For example, a PVA-based polarizer is obtained by allowing iodine or a dichromatic dye to be absorbed on polyvinyl alcohol (PVA) film, followed by uniaxial orientation by stretching. In such a polarizing plate, if moisture permeability of the polarizer protective film is high, dissociation of PVA or iodine ion in the polarizer can affect polarizing performance.
Although triacetyl cellulose (TAC) films are generally used as polarizer protective film from the viewpoint of transparency, appearance, and easy adhesion to the polarizer, the moisture permeability thereof (about 300 g/m2/24 hours) may be insufficient to protect the polarizer in high humidity, especially as application fields of viewing displays become wider, and requirements for polarizing plates become more severe as a result.
In addition, hard coat processing is commonly applied for the purpose of protecting the surface of the polarizing plate. This hard coat layer is typically formed by a method in which a curable coated film with high hardness is added on the surface of the protective film. It would be advantageous to provide a protective film with sufficient hardness to eliminate the requirement for a hard coat layer.